Probably for erotica, it's best to keep physical description to a minimum, as others have suggested. Different people find different things attractive. For example, I wouldn't be at all interested in IDCrewDawg's example. Too much emphasis on muscle and chest, etc. for me. I'm much more drawn to men with a dancer's body, and I'm particularly partial to men who do have a bit of curve - usually their butt. Focusing on the usual triangular shape tends to turn me off.

Overall, I find physical descriptions that involve emotions: voice, facial expression, etc. much more interesting than a something that's purely physical.

I can't think of an example offhand.

Also, sensory details are useful: I like IDCrewDawg's note of the musky scent. Add in all the senses, and since we're dealing with erotica, don't forget taste. What's the texture of the skin, lips? The timber of the voice or the sound of his hand swooshing through the air, the gasps in his breath? The scent of his breath (not always great) and skin? The taste of his tongue... The flash in his eyes, the widening of them in sudden fear, closing them in pleasure.

And it really depends a lot on point of view. Anything can be erotic if your point of view character finds it erotic and can show this eroticism. Similarly, you're not going to know much about what the point of view character looks like to the other character(s). So think: what does *this* character find erotic, and then go from there.

I know that for me, the emotional situation and the BDSM elements are far more important than what someone looks like (I've dated, and enjoyed dating, two people who, on first site, I found absolutely repulsive compared to what I normally like), and that as I get to become attracted to someone, their appearance becomes attractive to me even if it wasn't at first.

I've also written some stories where ugliness was part of the point. Most of these were written before I knew about BDSM or what my particular tastes were, and in one non-consensual piece, a Goddess rapes a human in the guise of something he finds absolutely repulsive. The repulsivness was part of the punishment. Consider also things like Titania and Bottom in A Midsummer Night's Dream. Or alternatively, a dominant woman making the man ugly through clothes that aren't flattering, etc.

To revise my original thought: only include detailed physical appearance if it's important to the plot/eroticism of the piece. This can mean either the point of view character describing what it is about the appearance that turns him/her on or the opposite and having them have to deal with being turned on by someone they *don't* find physically attractive, and what that does, especially if this "ugly" thing (such as a wart) becomes something that later is the thing that turns them on through remembering the experience.